diff --git a/src/app/utils/sort.test.ts b/src/app/utils/sort.test.ts
new file mode 100644
index 000000000..22cb23016
--- /dev/null
+++ b/src/app/utils/sort.test.ts
@@ -0,0 +1,56 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import type { MatrixClient } from 'matrix-js-sdk';
+import {
+  byTsOldToNew,
+  byOrderKey,
+  factoryRoomIdByUnreadCount,
+  factoryRoomIdByActivity,
+  factoryRoomIdByAtoZ,
+} from './sort';
+
+test('byTsOldToNew sorts ascending by timestamp', () => {
+  assert.ok(byTsOldToNew(1, 2) < 0);
+  assert.ok(byTsOldToNew(5, 3) > 0);
+  assert.equal(byTsOldToNew(2, 2), 0);
+  assert.deepEqual([30, 10, 20].sort(byTsOldToNew), [10, 20, 30]);
+});
+
+test('byOrderKey: undefined sorts last, otherwise lexical', () => {
+  assert.equal(byOrderKey(undefined, undefined), 0);
+  assert.equal(byOrderKey('a', undefined), -1); // defined before undefined
+  assert.equal(byOrderKey(undefined, 'a'), 1);
+  assert.equal(byOrderKey('a', 'b'), -1);
+  assert.equal(byOrderKey('b', 'a'), 1);
+  // equal non-empty keys return 1 (not 0) — there is no equality branch for two
+  // present keys, so a stable sort keeps input order for equal keys.
+  assert.equal(byOrderKey('a', 'a'), 1);
+  assert.deepEqual(['c', undefined, 'a', 'b'].sort(byOrderKey), ['a', 'b', 'c', undefined]);
+});
+
+test('factoryRoomIdByUnreadCount sorts by unread count descending', () => {
+  const counts: Record<string, number> = { r1: 0, r2: 5, r3: 2 };
+  const cmp = factoryRoomIdByUnreadCount((id) => counts[id]);
+  assert.deepEqual(['r1', 'r2', 'r3'].sort(cmp), ['r2', 'r3', 'r1']);
+});
+
+test('factoryRoomIdByActivity sorts most-recently-active first', () => {
+  const ts: Record<string, number> = { old: 100, new: 300, mid: 200 };
+  const mx = {
+    getRoom: (id: string) => (id in ts ? { getLastActiveTimestamp: () => ts[id] } : null),
+  } as unknown as MatrixClient;
+  const cmp = factoryRoomIdByActivity(mx);
+  assert.deepEqual(['old', 'new', 'mid'].sort(cmp), ['new', 'mid', 'old']);
+  // a room the client can't resolve sinks to the bottom
+  assert.deepEqual(['missing', 'new'].sort(cmp), ['new', 'missing']);
+});
+
+test('factoryRoomIdByAtoZ sorts case-insensitively and ignores leading #', () => {
+  const names: Record<string, string> = { a: 'Banana', b: 'apple', c: '#Cherry' };
+  const mx = {
+    getRoom: (id: string) => ({ name: names[id] ?? '' }),
+  } as unknown as MatrixClient;
+  const cmp = factoryRoomIdByAtoZ(mx);
+  // apple < Banana < Cherry (# stripped, case-insensitive)
+  assert.deepEqual(['a', 'b', 'c'].sort(cmp), ['b', 'a', 'c']);
+});